[25.07] On the Controversy between Observations and Dynamical Modelling of Capturing Trojans by a Growing Proto-Jupiter

According to a widely accepted scenario, planetesimals were
trapped in the Jupiter Trojan regions around L4 and L5 due
to the changing gravity field induced by the mass growth of
proto--Jupiter. Dynamical models yield final orbits for the
captured Trojans with large libration amplitudes and low
inclinations. The observed Trojan orbits are instead on low
libration--high inclination orbits. We have studied
complementary dynamical and physical processes that can
reconcile the predictions of the mass growth model for the
capture of Trojans with observations.

Mutual collisions between planetesimals surrounding the
growing Jupiter cause early trapping into Trojans orbits of
numerous bodies, as predicted theoretically by Shoemaker et
al (1989). During the final rapid growth of Jupiter by gas
infall, the libration amplitudes of the orbits of these
bodies are reduced by the shrinking of the zero--velocity
curves around the Lagrangian points. Even the coupling of
collisional effects and mass growth is able to produce a
population of small librators. We will show the results of
numerical simulations that include both the effects of
collisions, mass growth of the planet, and gas drag. The
efficiency of the mechanism is also estimated.

The high inclinations of Jupiter Trojans are not well
understood. If Trojans were bodies trapped from the
planetesimal disk, they should have conserved their
primordial low inclination. Which mechanism stirred up their
inclinations? It has been suggested that secular resonances
can contribute to generate highly inclined bodies (Marzari
and Scholl, 2000). Alternatively, large planetary embryos
which formed during the runaway growth in the Jupiter region
may have excited the inclinations of the Trojans by close
encounters and collisions similar to the mechanism described
by Petit et al. (1999) for the main belt asteroids. After a
few million years, these big embryos escaped from the Trojan
swarms either by natural instability or by dynamical
friction. We discuss the implications of this model.